Videos are in practice very often manipulated, stored and exchanged in a compressed format (MPEG 1, MPEG2, MPEG4-H264, divX, VC1, DV25 etc.), which makes it possible to reduce the transmission bit rate, the size of the storage space or the processing time. There is often a desire to watermark these videos: for example, for a VoD (Video On Demand) application, there is a desire to watermark each of the streams sent with a unique identifier (fingerprint) for each recipient (so that, in the event of piracy, the guilty recipient can be found). The videos are, in this application, stored and sent in compressed format (e.g MPEG2 or H264). The watermark is inserted just before the file is downloaded by a user who has requested it. It would then be ineffective watermark the video in its pixel form: it would need to be decompressed, watermarked and recompressed. Apart from an excessive overhead in computation time, the act of decompressing/recompressing the video adversely affects its visual quality and weakens the watermark that has been inserted.
In addition to the universal requirements for invisibility, ruggedness and the capacity to be embedded, a stream watermarking system also mostly needs to be quick to write, and not to increase the size of the video stream, and even produce a stream of a size that is strictly identical to the original stream. This last requirement is difficult to satisfy, because any change to the image data itself can result in very major changes to the video stream and therefore, possibly, modify the size thereof. In general, the act of watermarking a stream increases its size, which causes problems when the bit rate in the networks is limited.